Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$110.73	11.600%	$123.5747	$123.57	$123.55	$123.60
Purchase #2	$237.60	7.382%	$255.1396	$255.14	$255.15	$255.10
Purchase #3	$143.42	6.233%	$152.3594	$152.36	$152.35	$152.40
Purchase #4	$244.28	10.521%	$269.9807	$269.98	$270.00	$270.00
Purchase #5	$27.26	5.108%	$28.6524	$28.65	$28.65	$28.70
Purchase #6	$80.43	10.736%	$89.065	$89.07	$89.05	$89.10
Purchase #7	$45.71	12.701%	$51.5156	$51.52	$51.50	$51.50
7 purchase totals =	$889.43		$970.2874	$970.29	$970.25	$970.40